Channel monitoring by a multichannel selective call receiver

ABSTRACT

A multichannel selective call receiver ( 10 ) includes-a receiver ( 11 ), a controller ( 16 ), a baud detector ( 17 ) and a memory ( 18 ). The controller is adapted to control the receiver in receiving information on a channel ( 14 ). The information on the channel includes mandatory frames having information fields. If the information fields in a mandatory frame on the channel do not indicate more information for the multichannel selective call receiver in the rest of the mandatory frame, the controller controls the receiver to receive information on other channels ( 15 ) during the rest of the mandatory frame. The information on the channel and the other channels is processed in accordance with channel priority as indicated in a channel list stored in the memory.

FIELD OF THE INVENTION

This invention relates to selective call receivers, such as pagers,operating in a communication environment. In particular, this inventionrelates to, but is not necessarily limited by, channel monitoring by amultichannel selective call receiver operating in a communicationenvironment.

BACKGROUND OF THE INVENTION

Selective call receivers, such as pagers, of a selective call systemreceive information transmitted on carrier frequencies or channelswithin a communication environment. Such information is typicallyformatted according to messaging protocols defined for the selectivecall system. For example, Motorola's FLEX™ selective call system has amessaging protocol in which information is grouped into frames which arethen A transmitted as a cycle. A FLEX™ cycle has one hundred and twentyeight frames of which some are mandatory frames transmitted at the startof the FLEX™ cycle. Each of the mandatory frames is divided intoinformation fields. Information fields at the start of a mandatory framecan point to more information for a selective call receiver in the restof the mandatory frame. For example, the address field can address oneor more selective call receivers which will have more informationprovided by the rest of the mandatory frame.

Receiving information from a FLEX™ cycle requires a selective callreceiver to synchronize to the FLEX™ cycle to monitor for theinformation. Synchronizing has to be attained at or before the mandatoryframes to receive information from the information fields of suchframes. Upon processing the mandatory frames, other information, such asassigned frames that provide information specifically for the selectivecall receiver, can be determined to receive more information from theFLEX™ cycle. In a FLEX™ communication environment that supportsmultichannel selective call receivers, FLEX™ cycles are synchronouslytransmitted on different channels by referencing such cycles to externaltime signals provided by, for example, a Global Positioning System.These multichannel selective call receivers are supported by what isreferred to as a FLEX™ roaming system. Channels for multichannelselective call receivers in the FLEX™ roaming system are also known asroaming channels.

Determining which channel to monitor is critical for multichannelselective call receivers in a FLEX™ roaming system as information can bereceived from different FLEX™ cycles transmitted concurrently ondifferent roaming channels. Each of these different roaming channelsshould be monitored quickly as there can be a problem of not detectinginformation transmitted on another. Furthermore, invalid channels whichare not roaming channels of the FLEX™ roaming system can provide FLEX™cycles that may be inadvertently detected. Such invalid channels shouldbe quickly distinguished from valid channels that can provideinformation to the multichannel selective call receivers.

SUMMARY OF THE INVENTION

It is an object of this invention to overcome or at least alleviate atleast one of the problems associated with channel monitoring by amultichannel selective call receiver operating in a communicationenvironment.

According to one aspect of the invention, there is provided amultichannel selective call receiver comprising:

a receiver for receiving information on a channel, said informationbeing formatted as a cycle having a plurality of frames including atleast one mandatory frame having an address field; and

processing means coupled to said receiver,

wherein said processing means is adapted to control said receiver toreceive information on other channels within said mandatory frame whensaid address field does not address said multichannel selective callreceiver in said mandatory frame.

Preferably, said processing means can be further adapted to control saidreceiver to receive information on said other channels following saidaddress field and within said mandatory frame.

Suitably, said processing means can comprise a controller coupled to abaud detector, said controller being adapted to control said bauddetector to perform baud detection of information.

Preferably, said processing means can further comprise a timer fordetermining lapse of a predetermined time period, said timer beingassociated with said baud detector.

Suitably, said processing means can comprise a memory for storing achannel list indicative of channel priority of said channel and saidother channels.

According to another aspect of the invention, there is provided a methodfor channel monitoring by a multichannel selective call receiver, saidmethod comprising the steps of:

receiving information on a channel, said information being formatted asa cycle having a plurality of frames including at least one mandatoryframe having an address field; and

controlling said receiver to receive information on other channelsduring said mandatory frame when said address field does not addresssaid multichannel selective call receiver in said mandatory frame.

Preferably, said step of controlling can comprise the step ofdetermining whether remaining duration of said mandatory frame issufficient for a baud detection.

Suitably, said step of controlling can further comprise the step ofselecting a next channel for said baud detection when remaining durationof said mandatory frame is sufficient, said next channel being of ahigher or equal priority as indicated within a channel list stored in amemory.

Preferably, said step of controlling can further comprise the step ofmarking said next channel for a synchronization field sample when saidbaud detection determines that said next channel may be a valid channel.

Suitably, said step of controlling can further comprise the step ofsampling a synchronization field of a next available mandatory frame ofsaid next channel.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the invention and to put it into practical effect,reference will now be made to a preferred embodiment as illustrated withreference to the accompanying drawings in which:

FIG. 1 shows structure of a mandatory frame in a FLEX™ cycle inaccordance with a preferred embodiment of the invention.

FIG. 2 shows a block diagram of a multichannel selective call receiverfor receiving the FLEX™ cycle of FIG. 1; and

FIGS. 3a and 3 b are flow diagrams showing a method for operating themultichannel selective call receiver of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows structure of a mandatory frame 2 in a FLEX™ cycle 1 inaccordance with a preferred embodiment of the invention. FLEX™ cycle 1has at least one mandatory frame. Mandatory frame 2 has asynchronization field 3, a block information field 4, an address field5, a vector field 6 and a message field 7. Synchronization field 3 has abit in a frame information word for indicating that FLEX™ cycle 1 istransmitted on a channel which supports multichannel selective callreceivers as defined by the messaging protocol of FLEX™. In FLEX™,channels which support multichannel selective call receivers are alsoreferred to as roaming channels. In this specification, a valid channelis a roaming channel that can provide information with FLEX™ cycle 1 tomultichannel selective call receivers.

FIG. 2 shows a block diagram of a multichannel selective call receiver10 for receiving FLEX™ cycle 1 of FIG. 1 in a FLEX™ roaming system.Multichannel selective call receiver 10 comprises a receiver 11 andprocessing means 12. Receiver 11 couples to an antenna 13 for receivinginformation on different channels within a FLEX™ communicationenvironment of the FLEX™ roaming system. FIG. 2 shows two channels 14,15 as examples of the different channels. Processing means 12 comprisesa controller 16, a baud detector 17 and a memory 18. Memory 18 stores achannel list indicative of channel priority of the different channels.Controller 16 couples to control receiver 11 and baud detector 17 tomonitor the different channels.

When multichannel selective call receiver 10 is receiving at the startof a mandatory frame of a FLEX™ cycle on a channel, processing means 12is adapted to control receiver 11 to receive information on otherchannels during the mandatory frame when an address field of themandatory frame does not address multichannel selective call receiver 10in the mandatory frame. This is possible because the different channelsare roaming channels which support multichannel selective call receiver10 in the FLEX™ roaming system and FLEX™ cycles on such roaming channelsare synchronously transmitted. Therefore, multichannel selective callreceiver 10 needs only to synchronize to any FLEX™ cycle on any roamingchannel in the FLEX™ roaming system to be in synchronization with FLEX™cycles on other roaming channels.

In processing information from mandatory frames of FLEX™ cycles ofroaming channels in the FLEX™ roaming system, the inventionadvantageously uses information that has to be transmitted for each ofthe FLEX™ cycles in accordance with the messaging protocol of FLEX™.This provides a more reliable baud detection to be performed as suchinformation will be present in the mandatory frames for processing byprocessing means 12 of the invention. Furthermore, multichannelselective call receiver 10 in the invention monitors other channels onlywhen a channel that is currently monitored has no information within itsmandatory frames to provide to multichannel selective call receiver 10.The invention, therefore, does not affect multichannel selective callreceiver 10 in receiving information on such a channel.

FIGS. 3a and 3 b are flow diagrams showing a method 20 for operatingmultichannel selective call receiver 10. Starting at step 21, method 20proceeds to initialising baud detector 17 and a channel selector forselecting a channel from a channel list on which receiver 11 is toreceive information. The channel list is stored in memory 18 and isindicative of channel priority of the channel and other channels in thechannel list.

At decision step 23, controller 16 determines whether receiver 11 isreceiving information at the start of a mandatory frame of the channelselected at step 22. If decision step 23 is a “Yes”, controller 16checks at decision step 24 whether the mandatory frame is assigned forthe channel. If decision step 24 is a “Yes” to indicate that the channelis a valid channel, method 20 then proceeds to step 27 in whichcontroller 16 decodes the mandatory frame for more information. Ifdecision step 24 is a “No”, method then proceeds to decision step 25 inwhich controller 16 determines whether any channel is marked for “syncfield sample” (synchronization field sample).

A channel is marked for “sync field sample” when a baud detectionperformed on information from the channel indicates that such a channelmay be a valid channel. To confirm the channel as a valid channel,synchronization field 3 of a mandatory frame on the channel will have tobe sampled to detect the bit in the frame information word indicatingthat the channel is a roaming channel.

When method 20 begins from step 21, only one channel has been selectedby the channel selector and is being monitored so that decision step 25typically has a “No” outcome. However, for a “Yes” outcome from decisionstep 25, method 20 will proceed to sampling the channel marked for “syncfield sample”. Sampling a channel is according to channel priority asindicated in the channel list stored in memory 18. Channel priorityhelps in determining an order in which channels are sampled when morethan one channel is marked for “sync field sample”. Upon sampling achannel, a flag for marking the channel for “sync field sample” is resetto indicate that this channel has been sampled. For a “No” to decisionstep 25, method 20 proceeds to decision step 26 in which controller 16determines whether there is any channel of higher or equal priority tothe channel currently selected. If decision step 26 is a “Yes”, method20 proceeds to performing a “sync field sample” on the highest prioritychannel at step 29. If decision step 26 is a “No”, method 20 returns todecision step 23. Following a “No” from decision step 26, the channelthat has been selected by the channel selector will continue to beprocessed by processing means 12 for another mandatory frame fromdecision step 23 as described above.

From steps 27, 28, 29 method 20 proceeds to decision step 30. Bauddetector 17 is associated with a timer that is set to expire after lapseof a predetermined time period. This predetermined time period isvariable depending upon, for example, how many different channels thatmultichannel selective call receiver 10 has to monitor and,consequently, how many FLEX™ cycles are necessary so that baud detectioncan be performed on information on the different channels. Such a timercan be provided by, for example, timing circuitry within controller 16.Initialising of baud detector 17 at step 22 also includes initialisingthe timer.

Method 20 returns to decision step 23 with a “No” from decision step 30.However, with a “Yes” from decision step 30, method 20 proceeds todecision step 31 in which controller 16 determines whether remainingduration of a period of the mandatory frame is sufficient for bauddetection of information in the mandatory frame on one or more otherchannels. With a “No” from decision step 31 indicating that theremaining duration of the period of the mandatory frame is insufficient,method 20 returns to decision step 23. With a “Yes” from decision step31 indicating that baud detection of information in the mandatory frameon the one or more other channels is possible, method 20 proceeds todecision step 32 in which priority of a next channel in the channel listis determined. If the next channel has a higher or equal priority to thechannel currently being monitored, controller 16 then controls bauddetector 17 in performing a baud detection on the next channel in step33. Decision step 34 then determines whether this next channel passesthe baud detection. A “Yes” from decision step 34 indicates that thisnext channel may potentially have information for multichannel selectivecall receiver 10. Such a channel is, therefore, marked for a “sync fieldsample” to be performed at one of its mandatory frame. Marking a channelis by, for example, setting a flag to indicate that a “sync fieldsample” is required for the channel.

Following step 35 or a “No” outcome from decision steps 32 or 34, method20 checks at decision step 36 whether channels of higher or equalpriority in the channel list has been sampled with a baud detection.With a “No” from decision step 36, controller 16 then selects a nextchannel from the channel list at step 37 and returns method 20 todecision step 31. With a “Yes” from decision step 36, controller 16 thendetermines in decision step 38 whether any channel has been sampled andmarked for a “sync field sample”. A “Yes” from decision step 38 bringsmethod 20 back to decision step 23. Otherwise, a “No” from decision step38 brings method 20 back to step 22.

The invention advantageously provides for multichannel selective callreceiver 10 to sample different channels for information using otherinformation provided by mandatory frames which is always present on suchchannels. Also, by performing a baud detection prior to asynchronization field sample, only channels that may be valid channelswill be processed subsequently. This saves time as invalid channels willnot be inadvertently detected and unnecessarily monitored. Furthermore,the invention advantageously allows prioritization of different channelsso that a synchronization field at the start of a mandatory frame ismore efficiently used and, therefore, channel monitoring is moreeffective.

Although the invention has been described with reference to a preferredembodiment, it is to be understood that the invention is not restrictedto the embodiment described herein.

We claim:
 1. A multichannel selective call receiver comprising: areceiver for receiving information on a channel, said information beingformatted as a cycle having a plurality of frames including at least onemandatory frame having an address field; and processing means coupled tosaid receiver, said processing means being adapted to control saidreceiver to receive information on other channels following said addressfield and within said mandatory frame when said address field does notaddress said multichannel selective call receiver in said mandatoryframe.
 2. The multichannel selective call receiver as claimed in claim1, wherein said processing means comprises a controller coupled to abaud detector, said controller being adapted to control said bauddetector to perform baud detection of information.
 3. The multichannelselective call receiver as claimed in claim 2, wherein said processingmeans further comprises a timer for determining lapse of a predeterminedtime period, said timer being associated with said baud detector.
 4. Themultichannel selective call receiver as claimed in claim 1, wherein saidprocessing means comprises a memory for storing a channel listindicative of channel priority of said channel and said other channels.5. A method for channel monitoring by a multichannel selective callreceiver, said method comprising the steps of: receiving information ona channel, said information being formatted as a cycle having aplurality of frames including at least one mandatory frame having anaddress field; determining whether a remaining duration of saidmandatory frame is sufficient for a baud detection; and controlling saidreceiver to receive information on other channels during said mandatoryframe when said address field does not address said multichannelselective call receiver in said mandatory frame and said remainingduration of said mandatory frame is sufficient for a baud detection. 6.The method as claimed in claim 5 wherein said step of controllingfurther comprises the step of selecting a next channel for said bauddetection when remaining duration of said mandatory frame is sufficient,said next channel being of a higher or equal priority as indicatedwithin a channel list stored in a memory.
 7. The method as claimed inclaim 6 wherein said step of controlling further comprises the step ofmarking said next channel for a synchronization field sample when saidbaud detection determines said next channel may be a valid channel. 8.The method as claimed in claim 7 wherein said step of controllingfurther comprises the step of sampling a synchronization field of a nextavailable mandatory frame of said next channel.
 9. A method for channelmonitoring by a multichannel selective call receiver, said methodcomprising the steps of: receiving information on a channel, saidinformation being formatted as a cycle having a plurality of framesincluding at least one mandatory frame having an address field; andcontrolling said receiver to receive information on other channelsfollowing said address field and within said mandatory frame when saidaddress field does not address said multichannel selective call receiverin said mandatory frame.
 10. The method as claimed in claim 9, whereinsaid step of controlling further comprises the step of determiningwhether a remaining duration of said mandatory frame is sufficient for abaud detection.
 11. The method as claimed in claim 10 wherein said stepof controlling further comprises the step of selecting a next channelfor said baud detection when remaining duration of said mandatory frameis sufficient, said next channel being of a higher or equal priority asindicated within a channel list stored in a memory.
 12. The method asclaimed in claim 11 wherein said step of controlling further comprisesthe step of marking said next channel for a synchronization field samplewhen said baud detection determines said next channel may be a validchannel.
 13. The method as claimed in claim 12 wherein said step ofcontrolling further comprises the stop of sampling a synchronizationfield of a next available mandatory frame of said next channel.